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A longstanding mystery of the periodic table involves a group of unique elements called lanthanides. Also known as rare earth elements, or REEs, these silvery-white metals are challenging to isolate, given their very similar chemical and physical properties. This similarity makes it difficult to distinguish REEs from one other during extraction and purification processes. 

The world has come to depend on lanthanides’ magnetic and optical properties to drive much of modern technology — from medical imaging to missiles to smart phones. These metals also are in short supply, and because they’re found in minerals, lanthanides are difficult to mine and separate.   But that may change — thanks to a ɫ����-led discovery of a new oxidation state for a lanthanide element known as praseodymium.  

For the first time ever, praseodymium achieved a 5+ oxidation state. Oxidation occurs when a substance meets oxygen or another oxidizing substance. (The browning on the flesh of a cut apple, as well as rust on metal, are examples of oxidation.)
   
As far back as the 1890s, scientists suspected lanthanides might have a 5+ oxidation state, but  lanthanides in that state were too unstable to see, said , an associate professor in ɫ����’s . Discovering an element’s new oxidation state is like discovering a new element. As an example, La Pierre noted how plutonium’s discovery opened up a whole new area of the periodic table. 

“A new oxidation state tells us what we don’t know and gives us ideas for where to go,” he explained. “Each oxidation state of an element has distinct chemical and physical properties — so the first glimpse of a novel oxidation presents a roadmap for new possibilities.”
 
La Pierre and colleagues at University of Iowa and Washington State University recently discovered the 5+ oxidation state for lanthanides. 

“It was predicted but never seen until we found it,” said La Pierre, corresponding author of the study, “,” which was recently published in Nature Chemistry. “Lanthanides’ properties are really fantastic. We only use them commercially in one oxidation state — the 3+ oxidation state — which defines a set of magnetic and optical properties. If you can stabilize a higher oxidation state, it could lead to entirely new magnetic and optical properties.”
 
The researchers’ breakthrough will broaden the lanthanides’ technical applications in fields such as rare-earth mining and quantum technology and could lead to new electronic device architectures and applications. 

“Research in lanthanides has already yielded significant dividends for society in terms of technological development,” La Pierre added.
    
The researchers hope to discover new tools for mining critical REEs, including improving lanthanide separation and recycling processes. When mining these elements, lanthanide elements are frequently mixed together. The separation process is painstaking and inefficient, generating a significant amount of waste. But with increasing global demand for REEs, the U.S. faces a supply issue. Figuring out how to improve lanthanides separation, potentially through oxidation chemistry, will ultimately enhance the supply of these critical elements. 

— Anne Wainscott-Sargent
 
Funding: This research was supported by grants from the National Science Foundation and the U.S. Department of Energy.